Electrical Stimulation Treatment of Hypotension

ABSTRACT

Methods and devices for treating hypotension, such as in cases of shock, including septic shock and anaphylactic shock, wherein the treatment includes providing an electrical impulse to a selected region of the vagus nerve of a patient suffering from hypotension to block and/or modulate nerve signals that regulate blood pressure.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 11/592,095 filed Nov. 1, 2006 which claims the benefit of U.S.Provisional Patent Application Nos. 60/814,312, filed Jun. 16, 2006 and60/772,361, filed Feb. 10, 2006, the entire disclosures of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to the field of delivery of electricalimpulses to bodily tissues for therapeutic purposes, and morespecifically to devices and methods for treating conditions associatedwith hypotension by blocking and/or modulating signals in the vagusnerve, to facilitate stronger heart function and/or affectvasoconstriction.

There are a number of treatments for various infirmities that requirethe destruction of otherwise healthy tissue in order to affect abeneficial effect. Malfunctioning tissue is identified, and thenlesioned or otherwise compromised in order to affect a beneficialoutcome, rather than attempting to repair the tissue to its normalfunctionality. While there are a variety of different techniques andmechanisms that have been designed to focus lesioning directly onto thetarget nerve tissue, collateral damage is inevitable.

Still other treatments for malfunctioning tissue can be medicinal innature, in many cases leaving patients to become dependent uponartificially synthesized chemicals. Examples of this are anti-asthmadrugs such as albuterol, proton pump inhibitors such as omeprazole(Prilosec), spastic bladder relievers such as Ditropan, and cholesterolreducing drugs like Lipitor and Zocor. In many cases, these medicinalapproaches have side effects that are either unknown or quitesignificant, for example, at least one popular diet pill of the late1990's was subsequently found to cause heart attacks and strokes.

Unfortunately, the beneficial outcomes of surgery and medicines are,therefore, often realized at the cost of function of other tissues, orrisks of side effects.

The use of electrical stimulation for treatment of medical conditionshas been well known in the art for nearly two thousand years. It hasbeen recognized that electrical stimulation of the brain and/or theperipheral nervous system and/or direct stimulation of themalfunctioning tissue, which stimulation is generally a whollyreversible and non-destructive treatment, holds significant promise forthe treatment of many ailments.

Electrical stimulation of the brain with implanted electrodes has beenapproved for use in the treatment of various conditions, including painand movement disorders including essential tremor and Parkinson'sdisease. The principle behind these approaches involves disruption andmodulation of hyperactive neuronal circuit transmission at specificsites in the brain. As compared with the very dangerous lesioningprocedures in which the portions of the brain that are behavingpathologically are physically destroyed, electrical stimulation isachieved by implanting electrodes at these sites to, first senseaberrant electrical signals and then to send electrical pulses tolocally disrupt the pathological neuronal transmission, driving it backinto the normal range of activity. These electrical stimulationprocedures, while invasive, are generally conducted with the patientconscious and a participant in the surgery.

Brain stimulation, and deep brain stimulation in particular, is notwithout some drawbacks. The procedure requires penetrating the skull,and inserting an electrode into the brain matter using a catheter-shapedlead, or the like. While monitoring the patient's condition (such astremor activity, etc.), the position of the electrode is adjusted toachieve significant therapeutic potential. Next, adjustments are made tothe electrical stimulus signals, such as frequency, periodicity,voltage, current, etc., again to achieve therapeutic results. Theelectrode is then permanently implanted and wires are directed from theelectrode to the site of a surgically implanted pacemaker. The pacemakerprovides the electrical stimulus signals to the electrode to maintainthe therapeutic effect. While the therapeutic results of deep brainstimulation are promising, there are significant complications thatarise from the implantation procedure, including stroke induced bydamage to surrounding tissues and the neurovasculature.

One of the most successful modern applications of this basicunderstanding of the relationship between muscle and nerves is thecardiac pacemaker. Although its roots extend back into the 1800's, itwas not until 1950 that the first practical, albeit external and bulkypacemaker was developed. Dr. Rune Elqvist developed the first trulyfunctional, wearable pacemaker in 1957. Shortly thereafter, in 1960, thefirst fully implanted pacemaker was developed.

Around this time, it was also found that the electrical leads could beconnected to the heart through veins, which eliminated the need to openthe chest cavity and attach the lead to the heart wall. In 1975 theintroduction of the lithium-iodide battery prolonged the battery life ofa pacemaker from a few months to more than a decade. The modernpacemaker can treat a variety of different signaling pathologies in thecardiac muscle, and can serve as a defibrillator as well (see U.S. Pat.No. 6,738,667 to Deno, et al., the disclosure of which is incorporatedherein by reference).

Another application of electrical stimulation of nerves has been thetreatment of radiating pain in the lower extremities by means ofstimulation of the sacral nerve roots at the bottom of the spinal cord(see U.S. Pat. No. 6,871,099 to Whitehurst, et al., the disclosure ofwhich is incorporated herein by reference).

A further application is disclosed in U.S. Pat. No. 6,957,106 (“106”) toSchuler, et al., titled, “Implantable method to regulate blood pressureby means of coded nerve signals,” which is incorporated in its entiretyby reference. The '106 patent states that, “the electrical action forregulating cardiovascular blood pressure emerges from the medullopontinearea via the vagus nerve bundle.” Affecting the electrical action of thevagus nerve bundle therefore may affect regulation of blood pressure,making the vagus nerve a further subject of electrical stimulationstudy.

Most of the life support control of the human or animal body is via thevagus (or tenth cranial) nerve that exits from the medulla oblongata.This nerve is actually a long bundle of afferent and efferent neuronsthat travels over the internal body to most organs. The vagus nerveemerges from each side of the medulla and travels different routes tothe same target organs. Paralysis or severing the two vagus nerves atthe level of the medulla or neck is rapidly fatal.

Blood pressure is the pressure exerted by the blood on the walls of theblood vessels. Unless indicated otherwise, blood pressure refers tosystemic arterial blood pressure, i.e., the pressure in the largearteries delivering blood to body parts other than the lungs, such asthe brachial artery (in the arm). The pressure of the blood in othervessels is lower than the arterial pressure. Blood pressure values areuniversally stated in millimetres of mercury (mm Hg), and are alwaysgiven relative to atmospheric pressure. For example, the absolutepressure of the blood in an artery with mean arterial pressure stated as100 mm Hg, on a day with atmospheric pressure of 760 mm Hg, is 860 mmHg.

The systolic pressure is defined as the peak pressure in the arteriesduring the cardiac cycle; the diastolic pressure is the lowest pressure(at the resting phase of the cardiac cycle). The mean arterial pressureand pulse pressure are other important quantities. Typical values for aresting, healthy adult are approximately 120 mm Hg systolic and 80 mm Hgdiastolic (written as 120/80 mm Hg), with large individual variations.These measures of blood pressure are not static, but undergo naturalvariations from one heartbeat to another or throughout the day (in acircadian rhythm); they also change in response to stress, nutritionalfactors, drugs, or disease.

An instance of the connection between the vagus nerve and blood pressureregulation may be found in U.S. Pat. No. 5,707,400 (“′400”), to Terry,et al., titled, “Treating refractory hypertension by nerve stimulation,”which is incorporated in its entirety by reference. Hypertension (higherthan normal blood pressure) and its converse, hypotension (lower thannormal blood pressure), largely comprise the two sides of the coin thatrepresents the problems relating to blood pressure. Issuing relating tohypotension, its causes and effects, are discussed also in U.S. PatentApplication Number 20050283197 A1, to Daum, et al., titled, “Systems andmethods for hypotension,” which is incorporated in its entirety byreference.

Blood pressure exceeding normal values is called arterial hypertension.It itself is only rarely an acute problem, with the seldom exception ofhypertensive crisis, such as severe hypertension with acute impairmentof an organ system (especially the central nervous system,cardiovascular system and/or the renal system) and the possibility ofirreversible organ-damage. However, because of its long-term indirecteffects (and also as an indicator of other problems) it is a seriousworry to physicians diagnosing it. Persistent hypertension is one of therisk factors for strokes, heart attacks, heart failure, arterialaneurysms, and is the second leading cause of chronic renal failureafter diabetes mellitus.

All level of blood pressure puts mechanical stress on the arterialwalls. Higher pressures increase heart workload and progression ofunhealthy tissue growth (atheroma) that develops within the walls ofarteries. The higher the pressure, the more stress that is present andthe more atheroma tend to progress and the heart muscle tends tothicken, enlarge and become weaker over time.

Blood pressure that is too low is known as hypotension. Low bloodpressure may be a sign of severe disease and requires more urgentmedical attention. When blood pressure and blood flow is very low, theperfusion of the brain may be critically decreased (i.e., the bloodsupply is not sufficient), causing lightheadedness, dizziness, weaknessand fainting.

Sometimes the blood pressure drops significantly when a patient standsup from sitting. This is known as orthostatic hypotension; gravityreduces the rate of blood return from the body veins below the heartback to the heart, thus reducing stroke volume and cardiac output. Whenpeople are healthy, they quickly constrict the veins below the heart andincrease their heart rate to minimize and compensate for the gravityeffect. This is done at a subconscious level via the autonomic nervoussystem. The system usually requires a few seconds to fully adjust and ifthe compensations are too slow or inadequate, the individual will sufferreduced blood flow to the brain, dizziness and potential blackout.Increases in G-loading, such as routinely experienced by supersonic jetpilots “pulling Gs”, greatly increases this effect. Repositioning thebody perpendicular to gravity largely eliminates the problem.

Hypotension often accompanies and complicates many other systemic healthproblems, such as anaphylaxis and sepsis, leading to anaphylactic shockand septic shock, making it more difficult to address the underlyinghealth problem. For example, U.S. Patent Application Number 20050065553,Ben Ezra, et al., titled, “Applications of vagal stimulation,” which isincorporated in its entirety by reference, proposes to a method to treata patient's sepsis by applying an appropriately configured current tothe vagus nerve. However, when accompanied with refractory arterialhypotension, sepsis becomes septic shock.

Septic shock is a serious medical condition causing such effects asmultiple organ failure and death in response to infection and sepsis.Its most common victims are children and the elderly, as their immunesystems cannot cope with the infection as well as those of full-grownadults, as well as immunocompromised individuals. The mortality ratefrom septic shock is approximately 50%. Other various shock conditionsinclude: systemic inflammatory response syndrome, toxic shock syndrome,adrenal insufficiency, and anaphylaxis.

A subclass of distributive shock, shock refers specifically to decreasedtissue perfusion resulting in end-organ dysfunction. Cytokines TNFα,IL-1β, IL-6 released in a large scale inflammatory response may resultin massive vasodilation, increased capillary permeability, decreasedsystemic vascular resistance, and hypotension. Hypotension reducestissue perfusion pressure, and thus tissue hypoxia ensues. Finally, inan attempt to offset decreased blood pressure, ventricular dilatationand myocardial dysfunction will occur.

Myocardial dysfunction involves a decrease in overall myocardialperformance. The determinants of myocardial performance are heart rate,preload, afterload, and contractility.

Heart rate is a term used to describe the frequency of the cardiaccycle, usually in number of number of contractions of the heart (heartbeats) per minute. The heart contains two natural cardiac pacemakersthat spontaneously cause the heart to beat. These can be controlled bythe autonomic nervous system and circulating adrenaline.

The body can increase the heart rate in response to a wide variety ofconditions in order to increase the cardiac output (the amount of bloodejected by the heart per unit time). Exercise, environmental stressorsor psychological stress can cause the heart rate to increase above theresting rate. The pulse is the most straightforward way of measuring theheart rate, but it can be deceptive when some strokes do not lead tomuch cardiac output. In these cases (as happens in some arrhythmias),the heart rate may be considerably higher than the pulse.

Preload is theoretically most accurately described as the initialstretching of cardiac myocytes prior to contraction. Preload is thevolume of blood present in a ventricle of the heart, after passivefilling and atrial contraction. Preload is affected by venous bloodpressure and the rate of venous return. These are affected by venoustone and volume of circulating blood.

Afterload is the tension produced by a chamber of the heart in order tocontract. Afterload can also be described as the pressure that thechamber of the heart has to generate in order to eject blood out of thechamber. In the case of the left ventricle, the afterload is aconsequence of the blood pressure, since the pressure in the ventriclemust be greater than the blood pressure in order to open the aorticvalve. For instance, hypertension (increased blood pressure) increasesthe left ventricular afterload because the left ventricle has to workharder to eject blood into the aorta. This is because the aortic valvewon't open until the pressure generated in the left ventricle is higherthan the elevated blood pressure.

Contractility is the intrinsic ability of a cardiac muscle fiber tocontract at any given fiber length. If myocardial performance changeswhile preload, afterload and heart rate are all constant, then thechange in performance must be due to the change in contractility.Chemicals that affect contractility are called inotropic agents. Forexample drugs such as catecholamines (norepinephrine and epinephrine)that enhance contractility are considered to have a positive inotropiceffect. All factors that cause an increase in contractility work bycausing an increase in intracellular calcium concentration [Ca++] duringcontraction.

The concept of contractility was necessary to explain why someinterventions (e.g. an adrenaline infusion) could cause an increase inmyocardial performance even if, as could be shown in experiments, thepreload, afterload and heart rate were all held constant. Experimentalwork controlling the other factors was necessary because a change incontractility is generally not an isolated effect. For example, anincrease in sympathetic stimulation to the heart increases contractilityand heart rate. An increase in contractility tends to increase strokevolume and thus a secondary decrease in preload.

Accordingly, there is a need in the art for new products and methods fortreating the immediate symptoms of hypotension and shock.

SUMMARY OF THE INVENTION

The present invention involves products and methods of treatment ofhypotension utilizing an electrical signal that may be applied to thevagus nerve to temporarily block and/or modulate the signals in thevagus nerve. The present invention also encompasses treatment ofpathologies causing hypotension, both chronic and acute hypotension,such as in patients with thyroid pathologies and those suffering fromseptic shock. This treatment of hypotension may accompany treatment forother conditions, such as bronchial constriction, that also may occur insituations of shock.

In a first embodiment, the present invention contemplates an electricalimpulse delivery device that delivers one or more electrical impulses toat least one selected region of the vagus nerve to block and/or modulatesignals to the muscle fibers of the heart, facilitating contractility.

In a second embodiment, the present invention contemplates a device thatdelivers one or more electrical impulses to at least one selected regionof the vagus nerve to block and/or modulate signals to the fiberssurrounding the cardiac tissue, facilitating an increase in heartfunction, thereby raising blood pressure.

In a third embodiment, the present invention contemplates a device thatdelivers at least one electrical impulse to at least one selected regionof the vagus nerve to block and/or modulate signals to both the fiberssurrounding the cardiac tissue, facilitating an increase in heartfunction, thereby raising blood pressure, and the muscle fiberssurrounding the bronchi, facilitating opening of airways.

In yet another embodiment, methods in accordance with the presentinvention contemplate delivery of one or more electrical impulses to atleast one selected region of the vagus nerve to block and/or modulatesignals to the muscle fibers of the heart, facilitating contractility.

In another embodiment a method is provided of delivering one or moreelectrical impulses to at least one selected region of the vagus nerveto block and/or modulate signals to the fibers surrounding the cardiactissue, facilitating an increase in heart function, thereby raisingblood pressure.

In yet another embodiment, the present invention contemplates a methodof delivering at least one electrical impulse to at least one selectedregion of the vagus nerve to block and/or modulate signals to both thefibers surrounding the cardiac tissue, facilitating an increase in heartfunction, thereby raising blood pressure, and the muscle fiberssurrounding the bronchi, facilitating opening of airways.

It shall be understood that the activation of such impulses may bedirected manually by a patient suffering from hypotension, such asduring shock, depending on the embodiment.

Although the invention is not limited by any theory of operation, in oneor more embodiments of the present invention, it is believed that theimpulses may be applied in such a manner that the myocardium is relaxedto reduce the baseline level of tonic contraction, vasoconstrictionoccurs to increase blood pressure, and/or in cases of some shock, thesmooth muscle lining the bronchial passages is relaxed to relieve thespasms that occur, such as during anaphylactic shock. The impulses maybe applied by positioning leads on the nerves that control cardiacactivity, and bronchial activity respectively, such as the superior andinferior cardiac branches, and the anterior and posterior bronchialbranches, of the right and left branches of the vagus nerve, which joinwith fibers from the sympathetic nerve chain to form the anterior andposterior coronary and pulmonary plexuses. Leads may be positioned aboveboth the cardiac and pulmonary branches of the vagus nerve to include ablock and/or modulation of both organs. It shall also be understood thatleadless impulses as shown in the art may also be utilized for applyingimpulses to the target regions.

The mechanisms by which the appropriate impulse is applied to theselected region of the vagus nerve can include positioning the distalends of an electrical lead or leads in the vicinity of the nervoustissue controlling the myocardium, the vessels to/from the heart (toaffect vasodilation and/or vasoconstriction), and possibly pulmonarymuscles, which leads are coupled to an implantable or externalelectrical impulse generating device. The electric field generated atthe distal tip of the lead creates a field of effect that permeates thetarget nerve fibers and causes the blocking and/or modulating of signalsto the subject muscles.

The application of electrical impulses, either to the vagus nerve or thefibers branching off the vagus nerve to the cardiac muscles (andoptionally the bronchial muscles for increasing pulmonary function) tomodulate the parasympathetic tone in order to relax the myocardium,effect vasodilation/vasoconstriction, and optionally the bronchialmuscle, is more completely described in the following detaileddescription of the invention, with reference to the drawings providedherewith, and in claims appended hereto.

Other aspects, features, advantages, etc. will become apparent to oneskilled in the art when the description of the invention herein is takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purposes of illustrating the various aspects of the invention,there are shown in the drawings forms that are presently preferred, itbeing understood, however, that the invention is not limited by or tothe precise data, methodologies, arrangements and instrumentalitiesshown, but rather only by the claims of an issued utility application.

FIG. 1 is a diagrammatic view of the sympathetic and parasympatheticnerve systems.

FIG. 2 is a cross-sectional anatomical illustration of selected portionsof a neck, thoracic and abdominal region.

FIG. 3 illustrates a simplified view of the vagus nerve shown in FIGS. 1and 2.

FIG. 4 illustrates an exemplary electrical voltage/current profile for ablocking and/or modulating impulse applied to a portion or portions ofthe vagus nerve in accordance with an embodiment of the presentinvention.

FIGS. 5-13 graphically illustrate exemplary experimental data obtainedin accordance with multiple embodiments of the present invention.

FIGS. 14-19 graphically illustrate the inability of signals taught byU.S. patent application Ser. No. 10/990,938 to achieve the results ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

It shall be understood that the embodiments disclosed herein arerepresentative of preferred aspects of the invention and are so providedas examples of the invention. The scope of the invention, however, shallnot be limited to the disclosures provided herein, nor by theprovisional claims appended hereto.

It has been observed in the literature that the nervous system maintainsa balance of the signals carried by the sympathetic and parasympatheticnerves. The vagus nerve, as a source of a signal to constrict cardiacmuscle, is thought to provide a baseline level of tonicity in thecardiac muscles, in order to prevent the tissue from expanding too much,and thus is considered responsible for depressing blood pressure toprevent heart exhaustion and dangerous hypertension during extremeexertion.

Specifically, one or more embodiments of the present inventioncontemplate that the signals carried by the vagus (parasympathetic)nerve to cause a slowing of the heart, possibly in combination with aconstriction of the smooth muscle surrounding the bronchial passages.The sympathetic nerve fibers carry the opposing signals that tend tospeed up the heart rate, as well as open the bronchial passages. Itshould be recognized that the signals of the vagus nerve mediate aresponse similar to that of histamine, while the sympathetic signalsgenerate an effect similar to epinephrine. Given the postulated balancebetween the parasympathetic and sympathetic signals, removing theparasympathetic signal should create an imbalance emphasizing thesympathetic signal. Along these lines, scientific literature alsoindicates that severing the vagus nerve in dogs will raise the animals'heart rates, as well as open the bronchial passages, much the same waythat epinephrine does.

Now referring to FIGS. 1 and 2, the vagus nerve is shown in more detail.The vagus nerve is composed of motor and sensory fibers. The vagus nerveleaves the cranium and is contained in the same sheath of dura matterwith the accessory nerve. The vagus nerve passes down the neck withinthe carotid sheath to the root of the neck. Parasympathetic innervationof the heart is mediated by the vagus nerve. The branches ofdistribution of the vagus nerve include, among others, the superiorcardiac, the inferior cardiac, the anterior bronchial and the posteriorbronchial branches.

On the right side, the vagus nerve descends by the trachea to the backof the root of the lung, where it spreads out in the inferior cardiacbranch and the posterior pulmonary plexus. The right vagus innervatesthe Sinoatrial node. Parasympathetic hyperstimulation predisposes thoseaffected to bradyarrhythmias. On the left side, the vagus nerve entersthe thorax, crosses the left side of the arch of the aorta, forming thesuperior cardiac branch, and descends behind the root of the left lung,forming the posterior pulmonary plexus. The left vagus whenhyperstimulated predisposes the heart to Atrioventricular (AV) blocks.

In mammals, two vagal components have evolved in the brainstem toregulate peripheral parasympathetic functions. The dorsal vagal complex(DVC), consisting of the dorsal motor nucleus (DMNX) and itsconnections, controls parasympathetic function below the level of thediaphragm, while the ventral vagal complex (VVC), comprised of nucleusambiguous and nucleus retrofacial, controls functions above thediaphragm in organs such as the heart, thymus and lungs, as well asother glands and tissues of the neck and upper chest, and specializedmuscles such as those of the esophageal complex.

The parasympathetic portion of the vagus innervates ganglionic neuronswhich are located in or adjacent to each target organ. The VVC appearsonly in mammals and is associated with positive as well as negativeregulation of heart rate, bronchial constriction, vocalization andcontraction of the facial muscles in relation to emotional states.Generally speaking, this portion of the vagus nerve regulatesparasympathetic tone. Muscle tone (also known as residual muscletension) is the continuous and passive partial contraction of themuscles. The VVC inhibition is released (turned off) in states ofalertness. This in turn causes cardiac vagal tone to decrease and heartfunction to increase, and airways to open, to support responses toenvironmental challenges.

The parasympathetic tone is balanced in part by sympathetic innervation,which generally speaking supplies signals tending to expand themyocardium (and/or effect vasoconstriction), and/or to relax thebronchial muscles, so that over-contraction and over-constriction,respectively, do not occur. Overall, myocardium tone, vasodilation,vasoconstriction, and/or airway smooth muscle tone are dependent onseveral factors, including parasympathetic input, inhibitory influenceof circulating epinephrine, NANC inhibitory nerves and sympatheticinnervation of the parasympathetic ganglia. Stimulation of the vagusnerve (up-regulation of tone), such as may occur in shock, results in aheart rate decrease and airway constriction. In this context,up-regulation is the process by which the specific effect is increased,whereas down-regulation involves a decrease of the effect. In general,the pathology of shock appears to be mediated by inflammatory cytokinesthat overwhelm receptors on the nerve cells and cause the cells tomassively up-regulate the parasympathetic tone. On a cellular level,up-regulation is the process by which a cell increases the number ofreceptors to a given hormone or neurotransmitter to improve itssensitivity to this molecule. A decrease of receptors is calleddown-regulation.

For instance, sepsis is mediated by severe infection and may result in alarge scale inflammatory response that releases cytokines TNFα, IL-1β,IL-6 mediating massive vasodilation, increased capillary permeability,decreased systemic vascular resistance, and hypotension. By comparison,anaphylaxis appears to be mediated predominantly by the hypersensitivityto an allergen causing the massive overproduction of cholenergicreceptor activating cytokines that overdrive the otherwise normallyoperating vagus nerve to signal massive constriction of the airways.Drugs such as epinephrine drive heart rate up while also relaxing thebronchial muscles, effecting temporary relief of symptoms from theseconditions. As mentioned above, experience has shown that severing thevagus nerve (an extreme version of reducing the parasympathetic tone)has an effect similar to that of epinephrine and adrenaline on heartrate and bronchial diameter in that the heart begins to race(tachycardia) and the bronchial passageways dilate. However, simplydriving up the heart rate may not result in the desired increase inblood pressure, due to the other factors, discussed above, that affectblood pressure.

In accordance with at least one aspect of the present invention, thedelivery, in a patient suffering from shock, of an electrical impulsesufficient to block and/or modulate transmission of signals in the vagusnerve will result in raising the heart function, and thus the bloodpressure, and depending on the placement of the impulse, relaxation ofthe bronchi smooth muscle, dilating airways. Preferably, an increase inblood pressure without an increase in heart rate will result.

In accordance with at least one aspect of the present invention,blocking and/or modulating the signal in the vagus nerve to reduceparasympathetic tone provides an immediate emergency response, much likea defibrillator, in situations of shock, providing an immediate increaseof heart function. Moreover, the teachings of the present inventionpermit an immediate heart function increase to enable subsequent lifesaving measures that otherwise would be ineffective or impossible due toother physiological effects. Treatment in accordance with the presentinvention provides increased heart function, and optionallybronchodilation, for a long enough period of time so that administeredmedication such as epinephrine has time to take effect before thepatient suffers hypoxia.

The methods described herein of applying an electrical impulse to aselected region of the vagus nerve may further be refined such that theat least one region may comprise at least one nerve fiber emanating fromthe patient's tenth cranial nerve (the vagus nerve), and in particular,at least one of the superior cardiac branches thereof, or alternativelyat least one of the inferior cardiac branches thereof.

The cardiac plexus is situated at the base of the heart, and is dividedinto a superficial part, which lies in the concavity of the aortic arch,and a deep part, between the aortic arch and the trachea. The two partsare, however, closely connected.

The superficial part of the cardiac plexus lies beneath the arch of theaorta, in front of the right pulmonary artery. It is formed by thesuperior cardiac branch of the left sympathetic nerve and the lowersuperior cervical cardiac branch of the left vagus. The superficial partof the cardiac plexus gives branches (a) to the deep part of the plexus;(b) to the anterior coronary plexus; and (c) to the left anteriorpulmonary plexus.

The deep part of the cardiac plexus is situated in front of thebifurcation of the trachea, above the point of division of the pulmonaryartery, and behind the aortic arch. It is formed by the cardiac nervesderived from the cervical ganglia of the sympathetic, and the cardiacbranches of the vagus and recurrent nerves. The only cardiac nerveswhich do not enter into the formation of the deep part of the cardiacplexus are the superior cardiac nerve of the left sympathetic nerve, andthe lower of the two superior cervical cardiac branches from the leftvagus, which pass to the superficial part of the plexus.

As necessary, the impulse may be directed to a region of the vagus nerveto block and/or modulate both the cardiac and bronchial branches. Asrecognized by those having skill in the art, this embodiment should becarefully evaluated prior to use in patients known to have preexistingcardiac issues.

Further reference is now made to FIG. 3, which illustrates a simplifiedview of the vagus nerve shown in FIG. 2 and cardiac and pulmonarybranches thereof. Also shown is a vagus nerve stimulation (VNS) device300 for stimulation of the vagus nerve. VNS device 300 is intended forthe treatment of hypotension, and optionally bronchial constriction,associated, for example, with shock.

VNS device 300 may include an electrical impulse generator 310; a powersource 320 coupled to the electrical impulse generator 310; a controlunit 330 in communication with the electrical impulse generator 310 andcoupled to the power source 320; and electrodes 340 coupled to theelectrical impulse generator 310 for attachment via leads 350 to one ormore selected regions 200A, 200B of a vagus nerve 200 of a mammal. Thedevice 300 may be self-contained, as shown, or comprised of variousseparate, interconnected units. The control unit 330 may control theelectrical impulse generator 310 for generation of a signal suitable foramelioration of the hypotension when the signal is applied via theelectrodes 340 to the vagus nerve 200. It is noted that VNS device 300may be referred to by its function as a pulse generator.

In accordance with one embodiment, one or more electrical impulses aredirected to location A on or near the vagus nerve above the cardiacbranch. In this embodiment one or more electrical impulses areintroduced at the location A to block and/or modulate and/or inhibitup-regulation of the parasympathetic tone and affect an increase inheart function, and possibly a dilation of airways. Location B, forinstance, being below the cardiac branch, would have little effect oncardiac performance, but may be used to dilate airways.

In patients known to be subject to shock, such as anaphylactic shock,one or more electrical impulse emitting devices 300 may be implanted inone or more selected regions 200A of the vagus nerve 200. Device 300 maybe percutaneous for emergency applications, wherein device 300 maycomprise an electrode 340 powered via an external power source 320.

U.S. Patent Application Publications 2005/0075701 and 2005/0075702, bothto Shafer, both of which are incorporated herein by reference, relatingto stimulation of neurons of the sympathetic nervous system to attenuatean immune response, contain descriptions of pulse generators that may beapplicable to the present invention.

FIG. 4 illustrates an exemplary electrical voltage/current profile for ablocking and/or modulating impulse applied to a portion or portions ofthe vagus nerve in accordance with an embodiment of the presentinvention.

With reference to FIG. 4, application of a suitable electricalvoltage/current profile 400 for the blocking and/or modulating impulse410 to the portion 200A of the vagus nerve 200 may be achieved using apulse generator 310. In a preferred embodiment, the pulse generator 310may be implemented using a power source 320 and a control unit 330having, for instance, a processor, a clock, a memory, etc., to produce apulse train 420 to the electrode(s) 340 that deliver the blocking and/ormodulating impulse 410 to the nerve 200 via leads 350.

For percutaneous use, the VNS device 300 may be available to the surgeonas external emergency equipment. For subcutaneous use, the VNS device300 may be surgically implanted, such as in a subcutaneous pocket of theabdomen. The VNS device 300 may be powered and/or recharged from outsidethe body or may have its own power source 320. By way of example, theVNS device 300 may be purchased commercially. The VNS device 300 ispreferably programmed with a physician programmer, such as a Model 7432also available from Medtronic, Inc.

The parameters of the modulation signal 400 are preferably programmable,such as the frequency, amplitude, duty cycle, pulse width, pulse shape,etc. In the case of an implanted pulse generator, programming may takeplace before or after implantation. For example, an implanted pulsegenerator may have an external device for communication of settings tothe generator. An external communication device may modify the pulsegenerator programming to improve treatment.

The electrical leads 350 and electrodes 340 are preferably selected toachieve respective impedances permitting a peak pulse voltage in therange from about 0.2 volts to about 20 volts.

The blocking and/or modulating impulse signal 410 preferably has afrequency, an amplitude, a duty cycle, a pulse width, a pulse shape,etc. selected to influence the therapeutic result, namely blockingand/or modulating some or all of the vagus nerve transmissions. Forexample the frequency may be about 1 Hz or greater, such as betweenabout 25 Hz to 3000 Hz, or between about 1000 Hz to about 2500 Hz.(These are notably higher frequencies than typical nerve stimulation ormodulation frequencies.) The modulation signal may have a pulse widthselected to influence the therapeutic result, such as about 20 μS orgreater, such as about 20 μS to about 1000 μS. The modulation signal mayhave a peak voltage amplitude selected to influence the therapeuticresult, such as about 0.2 volts or greater, such as about 0.2 volts toabout 20 volts.

In accordance with a preferred embodiment, VNS devices 300 in accordancewith the present invention are provided in the form of a percutaneous orsubcutaneous implant that can be reused by an individual.

In accordance with another embodiment, devices in accordance with thepresent invention are provided in a “pacemaker” type form, in whichelectrical impulses 410 are generated to a selected region 200A of thevagus nerve 200 by VNS device 300 on an intermittent basis to create inthe patient a lower reactivity of the vagus nerve 200 to up-regulationsignals.

In accordance with another embodiment, devices 300 in accordance withthe present invention are incorporated in an endotracheal tube device toameliorate hypotension during surgery.

In a preferred embodiment one or more devices 300 are located in thedistal portion of an endotracheal tube to contact selected region 200Aof the vagus nerve 200 to impart appropriate electrical impulses todampen reactivity of the vagus nerve 200 to stimulus. In all cases ofpermanent implantation, however, the implanting surgeon should vary thesignal modulated by the control unit 330 and specific location of thelead 350 until the desired outcome is achieved, and should monitor thelong-term maintenance of this effect to ensure that adaptive mechanismsin the patient's body do not nullify the intended effects.

In addition, or as an alternative to the devices to implement themodulation unit for producing the electrical voltage/current profile ofthe blocking and/or modulating impulse to the electrodes, the devicedisclosed in U.S. Patent Publication No.: 2005/0216062 (the entiredisclosure of which is incorporated herein by reference), may beemployed. U.S. Patent Publication No.: 2005/0216062 discloses amulti-functional electrical stimulation (ES) system adapted to yieldoutput signals for effecting faradic, electromagnetic or other forms ofelectrical stimulation for a broad spectrum of different biological andbiomedical applications. The system includes an ES signal stage having aselector coupled to a plurality of different signal generators, eachproducing a signal having a distinct shape such as a sine, a square or asaw-tooth wave, or simple or complex pulse, the parameters of which areadjustable in regard to amplitude, duration, repetition rate and othervariables. The signal from the selected generator in the ES stage is fedto at least one output stage where it is processed to produce a high orlow voltage or current output of a desired polarity whereby the outputstage is capable of yielding an electrical stimulation signalappropriate for its intended application. Also included in the system isa measuring stage which measures and displays the electrical stimulationsignal operating on the substance being treated as well as the outputsof various sensors which sense conditions prevailing in this substancewhereby the user of the system can manually adjust it or have itautomatically adjusted by feedback to provide an electrical stimulationsignal of whatever type he wishes and the user can then observe theeffect of this signal on a substance being treated.

Prior to discussing experimental results, a general approach to treatinghypotension in accordance with one or more embodiments of the inventionmay include a method of (or apparatus for) treating hypotensionassociated with anaphylaxis, anaphylactic shock, or some other trigger,comprising applying at least one electrical impulse to one or moreselected regions of the vagus nerve of a mammal in need of relief ofhypotension.

The method may include: implanting one or more electrodes to theselected regions of the vagus nerve; and applying one or more electricalstimulation signals to the electrodes to produce the at least oneelectrical impulse. The one or more electrical stimulation signals maybe of a frequency between about 1 Hz to 3000 Hz, and have an amplitudeof between about 1-6 volts.

The one or more electrical stimulation signals may be of a frequencybetween about 750 Hz to 1250 Hz; or between about 10 Hz to 35 Hz. Theone or more electrical stimulation signals may be of an amplitude ofbetween about 0.75 to 1.5 volts, preferably about 1.0 volts. The one ormore electrical stimulation signals may be one or more of a full orpartial sinusoid, square wave, rectangular wave, and/or triangle wave.The one or more electrical stimulation signals may have a pulsed on-timeof between about 50 to 500 microseconds, such as about 100, 200 or 400microseconds.

The polarity of the pulses may be maintained either positive ornegative. Alternatively, the polarity of the pulses may be positive forsome periods of the wave and negative for some other periods of thewave. By way of example, the polarity of the pulses may be altered aboutevery second.

EXPERIMENTAL DATA

While up-regulating the signal provided by the sympathetic nerves mayaccomplish the desired treatment effect, the present invention suggeststhat a more direct route to immediately breaking the cycle ofhypotension is via the vagus nerve because the mode of action for thehypersensitivity response in hypotension is at the vagus nerve and notthrough the sympathetic nerves. Therefore, experiments were performed toidentify exemplary methods of how electrical signals can be supplied tothe peripheral nerve fibers that innervate and/or control the myocardium(and/or vasoconstriction) to (i) reduce the sensitivity of the muscle tothe signals of tonic contraction, (ii) to blunt the intensity of, orbreak the tonic over-contraction once it has been initiated, and/or(iii) to constrict the vessels to increase blood pressure.

In particular, specific signals, selected from within a range of knownnerve signals, were applied to the vagus nerves and/or the sympatheticnerves in guinea pigs, to produce selective interruption or reduction inthe effects of vagal nerve activity leading to attenuation ofhistamine-induced hypotension and bronchoconstriction.

Experimental Procedure 1

Male guinea pigs (400 g) were transported to the lab and immediatelyanesthetized with an i.p. injection of urethane 1.5 g/kg. Skin over theanterior neck was opened and the carotid artery and both jugular veinswere cannulated with PE50 tubing to allow for blood pressure/heart ratemonitoring and drug administration, respectively. The trachea wascannulated and the animal ventilated by positive pressure, constantvolume ventilation followed by paralysis with succinylcholine (10ug/kg/min) to paralyze the chest wall musculature to remove thecontribution of chest wall rigidity from airway pressure measurements.

Guanethidine (10 mg/kg i.v.) was given to deplete norepinephrine fromnerve terminals that may interfere with vagal nerve stimulation. Bothvagus nerves were exposed in the neck and connected to electrodes toallow selective stimuli of these nerves. Following 15 minutes ofstabilization baseline hemodynamic and airway pressure measurements weremade before and after the administration of repetitive doses of i.v.histamine.

Following the establishment of a consistent response to i.v. histamine,vagal nerve stimulation was attempted at variations of frequency,voltage and pulse duration to identity parameters that attenuateresponses to i.v. histamine. Hypotension and bronchoconstriction inresponse to i.v. histamine are known to be due both to direct muscleeffects and to stimulation of vagal nerves to release acetylcholine.

At the end of vagal nerve challenges, atropine was administered i.v.before a subsequent dose of histamine to determine what percentage ofthe histamine-induced hypotension and bronchoconstriction was vagalnerve induced. This was considered a 100% response. Success ofelectrical interruption in vagal nerve activity in attenuatinghistamine-induced hypotension and bronchoconstriction was compared tothis maximum effect. Euthanasia was accomplished with intravenouspotassium chloride.

The blood pressure and heart rate were measured to track the subjects'vital signs. In order to measure the bronchoconstriction, the airwaypressure was measured with two sensors. In all the following graphs, thetop line BP (red) shows blood pressure, second line AP1 (green) showsairway pressure, third line AP2 (blue) shows airway pressure on anothersensor, the last line HR is the heart rate derived from the pulses inthe blood pressure.

FIG. 5 graphically illustrates exemplary experimental data on guinea pig#5. The graphs of FIG. 5 show the effect of a 25 Hz, 400 μS, 1V squarewave signal applied to both left and right vagus nerve in guinea pig #5when injected with 8 μg/kg histamine to decrease blood pressure andincrease airway pressure. The first trough and peak, respectively, inblood and airway pressures are from histamine alone, the next peak andpeak, respectively, are histamine and signal applied. The blood pressureis clearly increased, but the heart rate is not affected, by the 25 Hz,400 μS, 1V square-wave signal on the vagus nerve. It also is clearlyshown that the increase in airway pressure due to histamine is reducedin the presence of the 25 Hz, 400 μS, 1V square wave on the vagus nerve.

FIG. 6 graphically illustrates additional exemplary experimental data onguinea pig #5. The graphs of FIG. 6 show the effect of a 25 Hz, 200 μS,1V square wave signal applied to both of the left and right vagus nervesin guinea pig #5 when injected with 8 μg/kg histamine. The first bloodpressure peak, without an effect on airway pressure, is signal alone.The second peak and peak, respectively, are from histamine and signalapplied simultaneously, whereas the third trough and peak, respectively,are from histamine alone. The blood pressure clearly is increased by the25 Hz, 200 μS, 1V square wave signal, without simply driving the heartrate higher (i.e., heart pumping stronger, not faster or constriction ofblood vessels). It also is shown clearly that the increase in airwaypressure due to histamine is reduced in the presence of the 25 Hz, 200μS, 1V square wave on the vagus nerve. It is clear that the bloodpressure increase and airway pressure reduction are even better with the200 μS pulse width than the 400 μS signal.

FIG. 7 graphically illustrates further exemplary experimental data onguinea pig #5. The graphs of FIG. 7 show repeatability of the effectseen in the previous graph. The animal, histamine and signal are thesame as the graphs in FIG. 6.

It is significant that the effects shown above were repeated severaltimes with this animal (guinea pig #5), without any loss of nerveactivity observed. We could move the electrodes proximally and distallyalong the vagus nerve and achieve the same effect. It was, therefore,concluded that the effect was being achieved by means other than simplydamaging the nerve.

FIG. 8 graphically illustrates subsequent exemplary experimental data onguinea pig #5. The graphs of FIG. 8 show the effect of a 25 Hz, 100 μS,1V square wave that switches polarity from + to − voltage every second.This signal is applied to both left and right vagus nerve in guinea pig#5 when injected with 8 μg/kg histamine. From left to right, thevertical dotted lines coincide with blood pressure/airway eventsassociated with: (1) histamine alone (blood pressure trough with a largeairway spike—followed by a very brief manual occlusion of the airwaytube); (2) histamine with a 200 μS signal applied (blood pressure peakwith a smaller airway spike); (3) a 100 μS electrical signal alone(blood pressure peak with no airway spike); (4) histamine with a 100 uSsignal applied (blood pressure peak with a smaller airway spike again);(5) histamine alone (blood pressure trough with a large airway spike);and (6) histamine with the 100 μS signal applied (blood pressure peakwith a smaller airway spike again).

The animal's blood pressure is substantially increased by this signal,but as with the prior animal (guinea pig #4), the heart rate is notaffected. The blood and airway pressure effects appear to be better withthe 100 μS pulse width than the 200 μS pulse width signal. This evidencestrongly suggests that the decrease in blood pressure due to histaminecan be effectively negated and overcome by the application of a 25 Hz,100 μS, 1V square wave with alternating polarity on the vagus nerve.This evidence also strongly suggests that the respective the increase inairway pressure can be significantly reduced by the application of a 25Hz, 100 μS, 1V square wave with alternating polarity on the vagus nerve.

FIG. 9 graphically illustrates exemplary experimental data on guinea pig#6. The graphs in FIG. 9 show the effect of a 25 Hz, 200 μS, 1V squarewave that switches polarity from + to − voltage every second. Thissignal is applied to both left and right vagus nerve in guinea pig #6when injected with 16 μg/kg histamine. Note that this animaldemonstrated a very high tolerance to the effects of histamine, andtherefore was not an ideal test subject for the histamine-inducedeffects. However, the animal did provide us with the opportunity to testthe signal-only effects on blood pressure and modification of signalparameters.

In this case, the first trough in blood pressure and peak in airwaypressure are from histamine alone, followed by a trough-peak paircorresponding to a brief manual occlusion of the airway. The next andfinal trough-then-peak of the blood pressure, accompanied by a peak inthe airway pressure, is histamine with the signal applied. It is clearlyshown that the blood pressure is increased by application of a 25 Hz,200 μS, 1V square-wave signal with alternating polarity on the vagusnerve, but again, the heart rate is not affected. Furthermore, theincrease in airway pressure due to histamine is reduced moderately inits peak, and most definitely in its duration, when in the presence ofthe 25 Hz, 200 μS, 1V square wave with alternating polarity on the vagusnerve.

FIG. 10 graphically illustrates additional exemplary experimental dataon guinea pig #6. As mentioned above, guinea pig #6 in the graphs ofFIG. 9 above needed more histamine than other guinea pigs (16-20 μg/kgvs 8 μg/kg) to achieve the desired increase in airway pressure. Also,the beneficial effects of the 1V signal were less pronounced in pig #6than in #5. Consequently, we tried increasing the voltage to 1.5V. Thefirst blood pressure trough and airway pressure peak is from histaminealone. A series of six manual occlusions of the airway tube followed,each causing a blood pressure trough and airway pressure spike. The nextand final blood pressure trough-then-peak and airway pressure peak arethe result of histamine with the 1.5V, 25 Hz, 200 μS alternatingpolarity signal. The beneficial effects on the blood pressure, as wellas the airway pressure, are seen with slightly more impact, but notsubstantially better than the 1V.

FIG. 11 graphically illustrates further exemplary experimental data onguinea pig #6. Since guinea pig #6 was losing its airway reaction tohistamine, we tried to determine if the 25 Hz, 200 μS, 1V, alternatingpolarity signal could mitigate the effects of a 20V, 20 Hz airwaypressure stimulating signal to produce a simulated asthmatic orshock-like response. The first event of a blood pressure trough and anairway pressure peak corresponds to the 20V, 20 Hz stimulator signalapplied to simulate shock, then switched over to the 25 Hz, 200 μS, 1V,alternating polarity signal, causing the blood pressure to peak. Thesecond event is the 20V, 20 Hz signal alone, causing a major butrebounding blood pressure trough and an airway pressure peak.

The blood pressure increase after application of the 25 Hz, 200 μS, 1Vsignal during the first event caused a visible benefit over no signalduring the second event. Overall, the effects of the first event lookmodestly reduced and narrower than those of the second event. The 25 Hz,200 μS, 1V signal may have some beneficial airway pressure reductionafter electrical stimulation of airway constriction. Notably, in boththe first and second events, the simulated shock-signal momentarilyinterfered with the heart rate, until equilibrium could again bereached. After the second event, a brief manual occlusion occurred,spiking the airway pressure and depressing the blood pressure.

On animal #6 we investigated which branch of the vagus nerve had themost effect on the blood pressure. We found that the right branchstimulated with the 25 Hz, 1V, 200 μS signal was responsible for thevast majority of the blood pressure increase. Stimulating the left vagusdid not measurably affect the blood pressure.

FIG. 12 graphically illustrates subsequent exemplary experimental data.On guinea pig #6 we also investigated the effect of the 1V, 25 Hz, and200 μS alternating polarity signal on blood pressure. After a briefapplication of histamine and the asthma/shock-simulating signal, causinga corresponding blood pressure trough and airway pressure peak, the 1V,25 Hz, and 200 μS alternating polarity signal was applied for 10minutes. The charts show the sustained increase in blood pressurethroughout the 10-minute signal application. Even after application ofthe signal for 10 minutes continuously, there was no loss of nerveconduction or signs of damage.

In contrast to the previous animals, guinea pig #7 was in distress fromthe initial preparation before any tests were run. Its blood pressurewas low and sinking while the airway pressure was uneven and rising.This animal's blood pressure could be raised with our 25 Hz, 1V, 200 μSsignal but without the signal, it kept falling. When the blood pressurewas almost gone, we kept our signal on for several minutes and kept theanimal alive for that time.

FIG. 13 graphically illustrates exemplary experimental data on guineapig #8. The graph below shows the effect of a 25 Hz, 200 μS, 1V squarewave that switches polarity from + to − voltage every second. Thissignal is applied to both left and right vagus nerve in guinea pig #8when injected with 12 μg/kg histamine. The first trough-peak pair inblood and airway pressures is from histamine alone, whereas the nexttrough-peak pair represents a manual occlusion. The third pair, a bloodpressure trough-then-peak and an airway pressure peak, is histamine withthe signal applied. The blood pressure is clearly increased by thissignal, 25 Hz, 200 μS, 1V square wave with alternating polarity, but theheart rate is not affected. It clearly is shown also that the increasein airway pressure due to histamine is reduced in the presence of the 25Hz, 200 μS, 1V square wave with alternating polarity on the vagus nerve.We have reproduced this effect multiple times, on 4 different guineapigs, on 4 different days.

The blood pressure in guinea pigs can be significantly increased byapplying appropriate electrical signals to the vagus nerve. Likewise,airway constriction induced by histamine in guinea pigs can besignificantly reduced by applying appropriate electrical signals to thevagus nerve.

With a 25 Hz, 1V, 100-200 μS signal applied to the right branch or bothbranches of vagus nerve, a significant increase in guinea pig bloodpressure is observed. This has been repeated on multiple animals manytimes. There is no evidence of nerve damage. Such a signal may beapplied in the treatment of low blood pressure in conditions such asseptic shock and anaphylactic shock.

The 25 Hz, 1V, 100-200 μS signal applied to the vagus nerve alsosignificantly reduced airway constriction due to histamine.

Application of the signal to the vagus nerve appears to have someeffects lasting long after the signal is removed. Specific, repeatableexperimentation may be done to substantiate these longer lastingeffects.

Additional testing on the guinea pig model may quantify the extent towhich longer lasting effects remain after stimulation is removed.

Experimental Procedure 2

In U.S. patent application Ser. No. 10/990,938 filed Nov. 17, 2004(Publication Number US2005/0125044A1), Kevin J. Tracey proposes a methodof treating many diseases including, among others, asthma, anaphylacticshock, sepsis and septic shock by electrical stimulation of the vagusnerve. However, the examples in the Tracey application use an electricalsignal that is 1 to 5V, 1 Hz and 2 mS to treat endotoxic shock, and noexamples are shown that test the proposed method on an asthma model, ananaphylactic shock model, or a sepsis model. The applicants of thepresent application performed additional testing to determine ifTracey's proposed method has any beneficial effect on blood pressure orbronchial constriction. The testing followed the model described above,which demonstrated the efficacy of the method used in accordance withthe present application. The applicants of the present applicationsought to determine whether Tracey's signals can be applied to the vagusnerve in guinea pigs to increase blood pressure and/or attenuatehistamine-induced bronchoconstriction.

Male guinea pigs (400 g) were transported to the lab and immediatelyanesthetized with an i.p. injection of urethane 1.5 g/kg. Skin over theanterior neck was opened and the carotid artery and both jugular veinsare cannulated with PE50 tubing to allow for blood pressure/heart ratemonitoring and drug administration, respectively. The trachea wascannulated and the animal ventilated by positive pressure, constantvolume ventilation followed by paralysis with succinylcholine (10ug/kg/min) to paralyze the chest wall musculature to remove thecontribution of chest wall rigidity from airway pressure measurements.

Guanethidine (10 mg/kg i.v.) was given to deplete norepinephrine fromnerve terminals that may interfere with vagal nerve stimulation. Bothvagus nerves were exposed and connected to electrodes to allow selectivestimuli of these nerves. Following 15 minutes of stabilization, baselinehemodynamic and airway pressure measurements were made before and afterthe administration of repetitive doses of i.v. histamine.

Following the establishment of a consistent response to i.v. histamine,vagal nerve stimulation was attempted at variations of 1 to 5 volts, 1Hz, 2 mS to identity parameters that attenuate responses to i.v.histamine. Bronchoconstriction in response to i.v. histamine is known tobe due to both direct airway smooth muscle effects and due tostimulation of vagal nerves to release acetylcholine.

At the end of vagal nerve challenges atropine was administered i.v.before a subsequent dose of histamine to determine what percentage ofthe histamine-induced bronchoconstriction was vagal nerve induced. Thiswas considered a 100% response. Success of electrical interruption invagal nerve activity in attenuating histamine-inducedbronchoconstriction was compared to this maximum effect. Euthanasia wasaccomplished with intravenous potassium chloride.

The blood pressure and heart rate were measured to track the subjects'vital signs. In order to measure the bronchoconstriction, the airwaypressure was measured in two places. In all the following graphs, thetop line BP (red) shows blood pressure, second line AP1 (green) showsairway pressure, third line AP2 (blue) shows airway pressure on anothersensor, the last line HR is the heart rate derived from the pulses inthe blood pressure.

FIG. 14 graphically illustrates exemplary experimental data from a firstexperiment on another guinea pig. The graph shows the effects ofTracey's 1V, 1 Hz, 2 mS waveform applied to both vagus nerves on theguinea pig. The first trough in blood pressure, corresponding to a firstpeak in airway pressure, is from histamine alone, followed by a briefmanual occlusion, after which Tracey's signal was applied for 10 minutesas proposed in Tracey's patent application. As seen from the secondhistamine-induced blood pressure trough and airway pressure peak, at theright of the graph, the signal has no noticeable effect on bloodpressure or airway pressure. The blood pressure actually rose after thesignal was turned off.

FIG. 15 graphically illustrates exemplary experimental data from asecond experiment on the guinea pig in FIG. 14. The graph shows theeffects of Tracey's 1V, 1 Hz, 2 mS waveform with the polarity reversed(Tracey did not specify polarity in the patent application) applied toboth vagus nerves on the guinea pig. Again, the signal has no beneficialeffect on blood or airway pressure. In fact, during application of thesignal, the blood pressure was slightly lower, and the signal did notkeep the blood pressure from falling when the histamine was applied.Moreover, the second airway peak from the signal and histaminecombination is actually higher than the first peak of histamine alone.

FIG. 16 graphically illustrates exemplary experimental data from a thirdexperiment on the guinea pig in FIG. 14. The graph shows the effects ofTracey's 1V, 1 Hz, 2 mS waveform applied to both vagus nerves on theguinea pig. Again, the signal has no beneficial effect on blood orairway pressure. Analogous to the results in FIG. 15, the signal did notmaintain the blood pressure when the histamine was applied. Instead, itincreases airway pressure and reduces blood pressure.

FIG. 17 graphically illustrates additional exemplary experimental datafrom an experiment on a subsequent guinea pig. The graph shows, fromleft to right, first a beneficial blood pressure increase from the 1.2V,25 Hz, 0.2 mS signal disclosed in the present application. Thesubsequent three electrical stimulation treatments are 1V, 5V, and 2.5Vvariations of Tracey's proposed signal. It is clear that the Traceysignals do not cause an increase in blood pressure, but ratherfrequently cause a decrease.

FIG. 18 graphically illustrates further exemplary experimental data fromadditional experiments using signals within the range of Tracey'sproposed examples. None of the signals proposed by Tracey had anybeneficial effect on blood pressure. Factoring in a potential range ofsignals, one experiment used 0.75V, which is below Tracey's proposedrange, but there was still no beneficial effect on blood pressure.

FIG. 19 graphically illustrates exemplary experimental data fromsubsequent experiments showing the effect of Tracey's 5V, 1 Hz, 2 mSsignal on histamine response. The blood pressure fell with applicationof the Tracey signal and fell even farther with application of thehistamine. It is clear that the airway pressure increase is even greaterwith the signal, and that blood pressure is decreased by the signal.

The full range of the signal proposed by Tracey in his patentapplication was tested in the animal model of the present application.No reduction in airway pressure was seen. No increase in blood pressurewas seen. Most of the voltages resulted in detrimental decreases inblood pressure and detrimental increases in airway pressure.

Experimental Procedure 3

While the above experiments were conducted by inducing hypotension(and/or bronchial constriction) using i.v. histamine, additional testdata were obtained in response to anaphylaxis. Fifteen male guinea pigs(400 g) were sensitized by the intraperitoneal injection of ovalbumin(10 mg/kg i.p. every 48 hrs for three doses). Three weeks later animalswere transported to the lab and immediately anesthetized with an i.p.injection of urethane 1.5 g/kg. Skin over the anterior neck was openedand the carotid artery and both jugular veins were cannulated with PE50tubing to allow for blood pressure/heart rate monitoring and drugadministration, respectively. The trachea was cannulated and the animalventilated by positive pressure, constant volume ventilation followed byparalysis with succinylcholine (10 ug/kg/min) to paralyzed chest wallmusculature to remove the contribution of chest wall rigidity fromairway pressure measurements. Both vagus nerves were isolated andconnected to shielded electrodes to allow selective stimuli of thesenerves in the manner disclosed in the one or more embodiments disclosedabove. Following fifteen minutes of stabilization, baseline hemodynamicand airway pressure measurements were made before and after theadministration of increasing concentrations of ovalbumin (0.001-1.0mg/kg i.v.). Following the increase in airway pressure and hypotensionaccompanying the anaphylactic response, vagal nerve modulation was madeat variations of frequency, voltage and pulse duration to identityparameters that attenuate the hypotensive and bronchoconstrictiveresponses. Euthanasia was accomplished with intravenous potassiumchloride.

With reference to FIG. 20, the top line (BP) shows blood pressure, thesecond line shows airway pressure (AP1), the third line shows airwaypressure (AP2) on another sensor, the fourth line is the heart rate (HR)derived from the pulses in the blood pressure. As a baseline of theanaphylactic reaction that is achieved in this model, the first guineapig's response to the ovalbumin was recorded without any electricalstimulation. The graph in FIG. 20 shows the effect of an injection of0.75 mg of ovalbumin. About five minutes after the injection, the bloodpressure dropped from 125 to 50 mmHg while the airway pressure increasedfrom 11 to 14 cm H₂O. This effect was sustained for over sixty (60)minutes with the blood pressure showing some recovery to 90 mmHg.

With reference to FIG. 21, another animal (guinea pig #2) was tested todetermine the effect of the signals that were shown to be effective inthe histamine induced asthma model (Experimental Procedure 1 above).FIG. 21 demonstrates the effect of a 25 Hz, 200 uS, 1.25V square wavesignal applied simultaneously to both left and right vagus nerves insensitized guinea pig #2 after injection with 1.125 mg ovalbumin tocause an anaphylactic response. The larger dose was used to cause a moresevere reaction. Starting from the left side of the graph, it may beseen that before electrical stimulation, the blood pressure was severelydepressed at 30 mmHg while the airway pressure was almost 22 cm H₂O (9.5cm increase over baseline). The first peak in blood pressure coincideswith the electrical signal applied to the vagus—the blood pressureincreased to 60 mmHg (a 100% increase) while the airway pressure reducedby 6.5 cm to about 15.5 cm H₂O (a 68% reduction). The next peak showsthe effect repeated. The other peaks show the effects of changing thesignal voltage—lowering the voltage results in reduced effectiveness.

With reference to FIG. 22, the effect of changing the signal frequencyand pulse width on blood pressure and airway pressure is shown. Thefirst peak in blood pressure coincides with a 15 Hz, 300 uS, 1.25Velectrical signal applied to both sides of the vagus—the blood pressurewas increased to 60 mmHg (a 70% increase) while the airway pressure wasreduced by 1.5 cm to about 17 cm H₂O (a 25% reduction). The next peakdemonstrates a 10 Hz signal—the beneficial effects are reduced comparedto 15 Hz. The other peaks show the effects of changing the signalfrequency and pulse width—lowering the frequency below 15 Hz or loweringthe pulse width below 200 uS results in reduced effectiveness. Thesignals between 15-25 Hz, and 200-300 uS maintain about the sameeffectiveness in decreasing the hypotensive and bronchoconstrictivesymptoms of anaphylaxis.

Conclusions that may be drawn from the above experimental data include:(1) That the airway constriction and hypotension caused by anaphylaxisin guinea pigs can be significantly reduced by applying appropriateelectrical signals to the vagus nerve. (2) That signals from 15 Hz to 25Hz, 200 uS to 300 uS, and 1.0V to 1.5V were equally effective. (3) Thata 25 Hz, 200 μS, 1.25V signal applied to the vagus nerve, airwayconstriction due to anaphylaxis was reduced up to 68%. This effect hasbeen repeated on several animals. (4) That the 25 Hz, 200 uS, 1.25Vsignal applied to the vagus nerve produces up to a 100% increase inblood pressure in an anaphylactic guinea pig experiencing severehypotension. This effect has been repeated on several animals. This mayhave applications in the treatment of other low blood pressureconditions such as septic shock. (5) That there is some evidence thatthe application of the signal to the vagus nerve may have the ability toshorten the duration of an anaphylactic episode.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. A method of treating a patient suffering from a disorder comprisingmodulating activity in at least one nerve in a selected region of aparasympathetic nervous system of the patient, the action potentialbeing sufficient to stimulate the nerve in the selected region of theparasympathetic nervous system and increase blood pressure in thepatient.
 2. The method set forth in claim 1 wherein the at least oneselected region comprises a region of a vagus nerve proximal to thecardiac branch of the vagus nerve.
 3. The method set forth in claim 1wherein the modulating step comprises applying an electrical impulse tothe at least one nerve in the selected region of the parasympatheticnervous system.
 4. The method set forth in claim 3 wherein theelectrical impulse is sufficient to increase blood pressure and maintaina stable heart rate.
 5. The method of claim 3 further comprising:implanting one or more electrodes to the selected regions of theparasympathetic nervous system; and applying one or more electricalstimulation signals to the electrodes to produce the at least oneelectrical impulse.
 6. The method of claim 3 further comprisingintroducing one or more electrodes percutaneous to the selected regionsof the parasympathetic nervous system and applying one or moreelectrical stimulation signals to the electrodes to produce the at leastone electrical impulse.
 7. The method of claim 3 wherein the electricalimpulse has a frequency between about 1 Hz to 3000 Hz, and an amplitudeof between about 1-12 volts.
 8. The method of claim 7, wherein theelectrical impulse has a frequency between about 750 Hz to 1250 Hz. 9.The method of claim 7 wherein the electrical impulse has a frequencybetween about 10 Hz to 35 Hz.
 10. The method of claim 7 wherein theelectrical impulse has an amplitude of between about 0.75 to 1.5 volts.11. The method of claim 7 wherein the electrical impulse has a pulsedon-time of between about 50 to 500 microseconds.
 12. The method of claim7 wherein the electrical impulse has a frequency of about 25 Hz, apulsed on-time of about 200-400 microseconds, and an amplitude of about1 volt.
 13. The method of claim 7 wherein the electrical impulse has afrequency of about 25 Hz, a pulsed on-time of between about 100 to 400microseconds, and an amplitude of about 1 volt.
 14. The method of claim1 wherein the disorder comprises hypotension.
 15. The method of claim 1wherein the disorder comprises shock.
 16. The method of claim 1 whereinthe disorder comprises septic shock.
 17. A method of treating a patienthaving a disorder comprising applying energy to at least one nerve in aparasympathetic nervous system of the patient, the energy beingsufficient to increase blood pressure while substantially maintaining aheart rate of the patient.
 18. The method set forth in claim 17 whereinthe at least one nerve comprises a region of a vagus nerve proximal tothe cardiac branch of the vagus nerve.
 19. The method set forth in claim17 wherein the applying energy step comprises applying an electricalimpulse to the at least one nerve in the selected region of theparasympathetic nervous system.
 20. The method set forth in claim 19wherein the electrical impulse is sufficient to increase blood pressureand maintain a stable heart rate.
 21. The method of claim 19 furthercomprising implanting one or more electrodes to the selected regions ofthe parasympathetic nervous system and applying one or more electricalstimulation signals to the electrodes to produce the at least oneelectrical impulse.
 22. The method of claim 19 further comprisingintroducing one or more electrodes percutaneous to the selected regionsof the parasympathetic nervous system and applying one or moreelectrical stimulation signals to the electrodes to produce the at leastone electrical impulse.
 23. The method of claim 19 wherein theelectrical impulse has a frequency between about 1 Hz to 3000 Hz, and anamplitude of between about 1-12 volts.
 24. The method of claim 23wherein the electrical impulse has a frequency between about 750 Hz to1250 Hz.
 25. The method of claim 23 wherein the electrical impulse has afrequency between about 10 Hz to 35 Hz.
 26. The method of claim 23wherein the electrical impulse has an amplitude of between about 0.75 to1.5 volts.
 27. The method of claim 23 wherein the electrical impulse hasa pulsed on-time of between about 50 to 500 microseconds.
 28. The methodof claim 23 wherein the electrical impulse has a frequency of about 25Hz, a pulsed on-time of about 200-400 microseconds, and an amplitude ofabout 1 volt.
 29. The method of claim 23 wherein the electrical impulsehas a frequency of about 25 Hz, a pulsed on-time of between about 100 to400 microseconds, and an amplitude of about 1 volt.
 30. The method ofclaim 17 wherein the disorder comprises hypotension.
 31. The method ofclaim 17 wherein the disorder comprises shock.
 32. The method of claim17 wherein the disorder comprises septic shock.